1. Field of the Invention
The present invention relates to isolated polypeptides having phytase activity and isolated polynucleotides encoding the polypeptides. The polypeptides are related to Citrobacter phytases derived from Citrobacter amalonaticus and Citrobacter gillenii, the amino acid sequence of which are shown in the appended sequence listing as SEQ ID NOs: 4 and 6. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods for producing and using the polypeptides, in particular within animal feed.
2. Description of the Related Art
Phytases are well-known enzymes, as are the advantages of adding them to foodstuffs for animals, including humans. Phytases have been isolated from very many sources, including a number of fungal and bacterial strains.
The acid histidine phosphatase appA of Escherichia coli as well as other gram-negative bacterial phytases are known to have a high specific activity.
The production by Citrobacter braakii YH-15 of an intracellular phytase is reported by Kim et al in Biotechnology Letters 25: 1231-1234, 2003. KR-2004-A-045267 and WO-2004/085638 disclose, as SEQ ID NO: 7, the amino acid sequence of a phytase from Citrobacter braakii YH-15, deposited as KCCM 10427. WO-2004/085638 was published on Jul. 10, 2004, viz. after the first priority date of the present application.
It is an object of the present invention to provide alternative polypeptides having phytase activity and polynucleotides encoding the polypeptides. The polypeptides of the invention are preferably of amended, more preferably improved, properties, for example of a different substrate specificity, of a higher specific activity, of an increased stability (such as acid-stability, heat-stability, and/or protease stability, in particular pepsin stability), of an amended pH optimum (such as a lower, or higher pH optimum), and/or of an improved performance in animal feed (such as an improved release and/or degradation of phytate).